The invention relates to a cryosurgical instrument and a method for separating a tissue sample from surrounding tissue of a biological tissue to be treated.
In cryosurgery, targeted controlled use of low temperatures are employed for devitalizing biological tissue. With flexible probes in particular, cryosurgery can be employed to remove foreign bodies from body cavities by freezing them solid to the cryoprobe or to a probe head, for example, foreign bodies which have been accidentally inhaled and must be removed from the respiratory tract. Cryosurgery is also suitable for collection of tissue samples (biopsy). In this context, a tissue sample can be frozen to the probe head and, after separation from the surrounding tissue, made accessible to an investigation.
There are various possibilities for deep-freezing in surgery; one is based on the Joule-Thomson effect: the atoms or molecules of an expanding gas below the inversion temperature counteract mutual attraction, such that the gas loses internal energy and cools. CO2 or N2O is conventionally employed as the expanding gas. These gases are—referred to as working or coolant gases.
Cryosurgical instruments of the type just described conventionally have a probe which can be brought to the tissue to be treated, and gas conduits which pass through the probe and release working gas into the inner lumen of the probe, where the working gas expands and consequently cools the tips of the probe (the probe head). Since the probe head is generally produced from a thermally conductive material, conduction of the heat of the tissue via the probe head and cooling is consequently ensured.
Tissue samples are usually collected by conventional routes by means of forceps biopsy. However, the specimen obtained is very small and is usually squeezed during removal. Biopsy by means of cryosurgery makes it possible to collect tissue samples considerably more efficiently. For the purpose of a biopsy, the cryoprobe (rigid or flexible) is conventionally guided to the desired place, e.g., in a gastrointestinal tract, via a working channel of an endoscope (which may also be either rigid or flexible). The tip of the probe or probe head is positioned on the tissue to be treated, e.g. a mucous membrane, and a desired region of tissue (the tissue sample) freezes solid on the probe head due to the cooling mechanisms described above. The tissue sample thus adheres to the cooled probe head and the frozen tissue can be detached from the surrounding tissue by a pulling movement.
The detachment requires application of a relatively high force, which must be applied by the user. This presents numerous problems if the tissue to be treated also moves during the separation operation (that is to say during a pulling movement). For example, a high pulling force cannot be exerted on the large intestine (if a biopsy sample is to be obtained from that organ), since the large intestine floats free in the abdomen. The necessary pulling force can be applied here—if at all—only in pulses. Because of this, injuries may occur in the surrounding tissue (from too much force being applied), or a tissue sample cannot be removed at all because the surrounding tissue yields too much. Under such conditions, the frozen tissue sample can prematurely detach from the probe head.
The invention is therefore based on the object of developing a cryosurgical instrument that can reliably remove a tissue sample without damage to the tissue or to the patient. The object of the invention is furthermore to provide a method for separating a tissue sample from surrounding tissue of a biological tissue to be treated, which solves the problems described.